Drones Are Branching Out

When the population of an animal species is significantly reduced or eliminated in an area, it can lead to many negative consequences. Through their removal from the food chain, other animals that depended on them as a food source must find new food sources or face extinction themselves. Furthermore, when predators are impacted, it can lead to a huge, unnatural proliferation of their prey species, which causes myriad problems for the environment. And when these environmental issues become severe, they also begin to impact humans, so it makes good sense for us to keep an eye on shifts in animal populations to take proactive steps to avoid ecological disasters.

This is easier said than done, however. It is notoriously difficult to collect data on the status and distribution of biodiversity, and accordingly, there is a scarcity of information available on the subject. One of the most promising methods of tracking biodiversity is through the collection of environmental DNA (eDNA). When an animal is present in an area, they leave behind small fragments of biological material containing DNA. Through the use of modern sequencing technologies, that DNA can be used to identify the species that it came from.

Samples of eDNA are easily collected in certain environments, like rivers and lakes, but on dry ground it is much more challenging due to the number of surfaces that it may be deposited on. Collecting material from tree canopies, in particular, has proven to be exceedingly difficult. To address this problem, a team of researchers at ETH Zurich have developed a novel drone design that is capable of landing on a wide variety of tree branch types, and collecting samples of eDNA in the process.

Two major problems needed to be solved for this drone to be successful — it needed a mechanism for making a safe landing on branches with varying levels of stiffness, and once contact with a branch was made, the drone needed to be able to collect eDNA samples. To make a clean landing, a flexible cage equipped with a force sensor was installed on the bottom of the drone. As the cage makes contact with a branch, it provides feedback about the interaction force between itself and the branch. This information is then fed into a haptic-based flight controller that replans waypoints for a soft landing.

Once the drone made good contact with a branch, collecting the eDNA was accomplished with a decidedly low-tech method — an adhesive tape affixed to the drone's force-sensing cage did the job of picking it up. Back in the lab, an Illumina MiSeq sequencer was used to sequence the DNA, then the OBITools software package was used to analyze the data and help determine what species were represented in the data. This provides the raw information researchers and conservationists need to help manage biodiversity.

To date, the drone has been tested on a total of seven tree species, and has been able to detect DNA from 21 distinct organisms, ranging from birds and mammals to insects. This is a big accomplishment, but it is only the beginning. The team is currently preparing for a competition in the rainforests of Singapore in which they will have 24 hours to collect eDNA from as many different species as they can. To be competitive, the researchers believe they will need to master landing on ten times as many types of trees as they have thus far. That is a lofty goal, but we think they will be able to pull it off.